Abstract

Host-parasite coevolution resulted in parasites optimizing their life cycle to obtain the most benefit from the host's behaviour. In passerines, for instance, some parasite groups have found means to match their egg shedding rhythms with the hours of the day when hosts are most active. In other bird groups, such as shorebirds, whose active times are not determined by day-night cycles but by other external factors such as tidal or lunar cycles, it is not yet known whether their endoparasites exhibit any predictable pattern in their egg shedding rhythms. Here we used a simple wild-caught (captive) system, to provide a first approximation of the parasite egg shedding patterns in wintering Rufous-chested dotterels (Zonibyx modestus). We collected faeces every 2 hours over 10 days until completing a 24-hour cycle, which was coupled with continuous video recordings to determine their feeding and drinking habits. Contrary to our expectation, we showed that parasite egg shedding followed a cyclic pattern, characterized by 2 peaks: one at midnight and another in the afternoon. Importantly, this shedding pattern was not related to the birds' feeding or drinking habits. We discuss possible environmental and physiological cues that parasites might use to trigger egg production, including the potential influence of tidal cycles on our results.